The control of the generation of foam from aqueous media during processing has been a continuing problem for many years. A number of chemical classes of active defoaming materials have been proposed for use in defoaming aqueous systems containing a variety of foaming materials. Such defoamers have been more or less effective depending on the concentration of foaming materials, the temperature of the aqueous media, the geometry of pumps, tanks or lines, the degree of mixing or agitation, and the mode of addition of an effective defoaming concentration of the defoaming composition. Control of the concentration of a defoaming composition in the aqueous medium is not always easily accomplished.
Conventionally, manual foam control has been attempted simply by visually detecting foam accumulation and reducing foam with a manual addition or episodic machine addition of defoaming agents into the aqueous medium.
Automatic foam control has also been attempted. Automatic foam detection is accomplished using ultrasonic detectors that can generate a signal proportional to foam height. Additionally, mechanical floating devices sensitive to foam height have also been used. Conductivity probes that can detect a difference in conductivity between foam and bulk aqueous solution have been used. Electric eyes that can be positioned to detect foam have been attempted. These systems have advantages and disadvantages. In certain cases, ultrasonic and other probes can be impaired by filming, soiling or foam adhesion when the probe comes in contact with foam or with foamable liquid. These control systems have resulted in loss of sensitivity and control, often resulting in failure to control foaming. Further, often ultrasonic and other devices that determine foam height often have problems in determining foam height as water levels fluctuate. The uncertainty in foam height caused by varying water levels can be a significant problem in long term consistent foam control. The industry has sought other methods for foam distribution and control.
Measurement of thermal energy by detecting and quantifying thermal infrared emissions is known in a variety of applications. Burbury et al., U.S. Pat. No. 5,446,516 teaches the use of temperature detection to maintain a reaction at an optimum temperature for best yield. Thomas et al., U.S. Pat. No. 5,417,233 teaches the use of an infrared beam in a low product alarm system. When a product is consumed, the product can no longer prevent an infrared beam from being detected. The detection of the beam then triggers a low product alarm to replace the consumed product. Jesadanont, U.S. Pat. No. 5,397,028 teaches a method for applying a liquid disinfectant to a users hands or other body part. The dispenser automatically senses the presence of the users hands or other similar body parts using an infrared sensing mechanism. Fender, U.S. Pat. No. 5,105,992 discloses a infrared sensor that detects a person hand to prompt dispensing a liquid soap. Kamysz et al., U.S. Pat. No. 5,305,915 uses an infrared sensor triggered dispenser to dispense soap to a user. Yashuhito, U.S. Pat. No. 5,392,646 teaches a method to sense the flow rate of a fluid using the temperature coefficient of resistance of an RC circuit. Feller, U.S. Pat. No. 5,390,541 similarly uses the modulation of a temperature sensor to predict flow rates. Hill et al., U.S. Pat. No. 5,273,060 uses an infrared sensor to detect a combustion or an explosion to prompt a fire extinguishing system. Holt, U.S. Pat. No. 5,263,112 uses an infrared fiber optic distribution sensor to detect the degree of twist or stress in a coiled optical cable. Cowan et al., U.S. Pat. No. 5,167,243 discloses a disinfestation system for agricultural products using a thermal conductivity detector to detect the concentration of carbon dioxide. Merkel, U.S. Pat. No. 5,026,989 teaches an infrared sensor used to detect the presence of a heated adhesive on a substrate to control adhesive amounts. Arai, U.S. Pat. No. 4,756,670 teaches a system using a ratio of heat dissipation coefficients of a pair of electrically heated matched temperature sensitive devices to detect flow in a liquid system. Kuehn, III et al., U.S. Pat. No. 4,392,782 teaches a system for controlling liquid level using vertically spaced thermistors that when immersed or cooled, result in a change of resistance, thus detecting the liquid level.
In summary, the prior art does contains teachings of a variety of uses for thermal detection of IR emission or radiation but does not contain a teaching that the different thermal properties of foam and an associated aqueous foam-generating liquid can be used to trigger the addition of a defoaming agent into an aqueous medium that can generate foam to control foaming.